The present invention relate to a positive radiation-sensitive mixture containing a compound which forms an acid under the action of actinic radiation and an acid-cleavable compound.
Positive radiation sensitive mixtures in which an acid is formed through the action of actinic radiation on a photoinitiator and the acid then, in a secondary reaction, renders the irradiated regions of an acid-cleavable material soluble in an appropriate developer have been known for some time.
Of the acid-cleavable materials employed hitherto in this area, the following have proven successful:
(a) those containing at least one orthocarboxylic ester and/or carboxamide acetal group, it being possible for the compounds to have a polymeric character and for the groups mentioned to occur as linking elements in the main chain or as lateral substituents,
(b) oligomeric or polymeric compounds containing recurring acetal and/or ketal groups in the main chain,
(c) compounds containing at least one enol ether or N-acyliminocarbonate group,
(d) cyclic acetals or ketals of .beta.-keto esters or amides, and
(e) compounds containing silyl ether groups.
As components of radiation-sensitive mixtures, acid-cleavable compounds of type (a) are described in detail in EP-A-0,022,571 and DE-A-2,610,842; mixtures which contain compounds of type (b) are described in DE-C-2,306,248 and DE-C-2,718,254; compounds of type (c) are mentioned in EP-A-0,006,626 and 0,006,627, compounds of type (d) are mentioned in EP-A-0,202,196: compounds belonging to type (e) are presented in DE-A3,544,165 and 3,601,264.
It was possible to achieve high radiation-sensitivity or photosensitivity in the case of the orthoesters, the amidoacetals, the enol ethers or the N-acyliminocarboxylic acids. However, such compounds have the disadvantage of poor shelf life.
Although oligomeric or polymeric compounds containing recurring acetal and/or ketal groups in the main chain have high radiation sensitivity, their field of use is limited because of their property as a plasticizer for the polymer matrix. In addition, the processing tolerances are low as a consequence of the choice of hydrolysis products.
The same inadequacies are also observed in polymeric, acid-cleavable materials described in US-A- 4,603,101. The monomers from which the polymeric materials mentioned therein are formed are tertiary-substituted organomethyl vinylaryl ethers, in particular tert-butyl vinylaryl ethers.
In order to link the factors "etching resistance" and "cleavage chemistry," compounds have been developed which contain acid-cleavable silyl ether groups. However, these compounds exhibit impaired shelf life and a noticeable impairment in radiation sensitivity.